An activated carbon, its impurity removal method and application in the preparation of electronic grade boric acid

Abstract

The present invention discloses an activated carbon, a method for removing impurities therefrom, and an application thereof in the preparation of electronic-grade boric acid. The method for removing impurities from the activated carbon provided by the present invention comprises the following steps: S1, primary cleaning: cleaning the activated carbon raw material with dilute sulfuric acid and soaking for 20 to 30 h to obtain primary activated carbon; S2, secondary cleaning: cleaning the primary activated carbon with ultrapure water to obtain secondary activated carbon and a washing solution, the conductivity of the washing solution being ≤10 μS; S3, tertiary cleaning: cleaning the secondary activated carbon with a boric acid solution to obtain the impurity-removed activated carbon and a boric acid washing solution, the difference between the total content of metal impurities in the boric acid washing solution and the total content of metal impurities in the boric acid solution being ≤30 μg / L. The present invention removes impurities from the activated carbon raw material by means of tertiary cleaning, and the obtained activated carbon has a low total content of metal impurities, and has good effects when used in the preparation process of electronic-grade boric acid, especially can achieve good TOC removal effects.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical processes, and particularly relates to an activated carbon, a method for removing impurities therefrom, and an application thereof in the preparation of electronic-grade boric acid. Background Art

[0002] With the rapid development of the electronics industry, especially the continuous progress of semiconductor and integrated circuit manufacturing technologies, the purity and quality requirements for electronic-grade chemicals are getting higher and higher. As one of the key electronic chemicals, electronic-grade boric acid plays a crucial role in the manufacturing process of electronic devices. Electronic-grade boric acid needs to have extremely high purity and low impurity content to meet the strict requirements of the electronics industry for chemicals.

[0003] Currently, the main methods for producing electronic-grade boric acid include oxidation neutralization method, electrolysis method, recrystallization method, extraction method, etc. Among them, the oxidation neutralization method is an easy-to-operate, low-cost and high-efficiency method. However, the purity of the boric acid product obtained by the current oxidation neutralization method is relatively low, and the contents of metal impurities and organic impurities are relatively high, especially the total organic carbon (TOC) content is high. It is difficult for the oxidation neutralization method to achieve a good TOC removal effect. Some studies have proposed using activated carbon for adsorption and impurity removal, but the activated carbon contains a large amount of impurities, especially the relatively high calcium and magnesium contents. It is difficult to achieve a good impurity removal effect using untreated activated carbon. Summary of the Invention

[0004] In order to overcome at least one of the above-mentioned problems existing in the prior art, one of the objectives of the present invention is to provide a method for removing impurities from activated carbon. Through specific impurity removal steps, activated carbon with high purity and low metal impurity content can be obtained, which can be used for the preparation of high-purity electronic-grade boric acid.

[0005] Another objective of the present invention is to provide an activated carbon obtained by the above-mentioned impurity removal method.

[0006] Another objective of the present invention is to provide an application of the above-mentioned activated carbon in the preparation of electronic-grade boric acid.

[0007] Another objective of the present invention is to provide a method for preparing electronic-grade boric acid using the above-mentioned activated carbon.

[0008] In order to achieve the above objectives, the technical solutions adopted by the present invention are as follows:

[0009] The first aspect of the present invention provides a method for removing impurities from activated carbon, comprising the following steps:

[0010] S1. Primary cleaning: The activated carbon raw material is cleaned with dilute sulfuric acid and soaked for 20 - 30 h to obtain primary activated carbon;

[0011] S2. Secondary cleaning: using ultrapure water to clean the primary activated carbon to obtain secondary activated carbon and a washing liquid, wherein the conductivity of the washing liquid is ≤10 μS;

[0012] S3, tertiary cleaning: washing the secondary activated carbon with a boric acid solution to obtain activated carbon and a boric acid washing solution after impurities are removed, wherein the difference between the total content of metal impurities in the boric acid washing solution and the total content of metal impurities in the boric acid solution is ≤30 μg / L.

[0013] The present invention adopts a three-stage cleaning step to remove impurities from the activated carbon. First, dilute sulfuric acid is used for sufficient cleaning to soak out some acid-soluble metal impurities. Then, ultrapure water is used for cleaning to further remove impurities and residual acid solution is washed away to avoid affecting subsequent steps. Finally, a boric acid solution is used for cleaning. Since boric acid is relatively advanced in the activated carbon adsorption order, the metal impurities adsorbed in the activated carbon can be replaced, so that the metal impurities are desorbed from the activated carbon, thereby achieving the effect of further purification of the activated carbon column. The difference between the total content of metal impurities in the finally obtained boric acid washing solution and the total content of metal impurities in the boric acid solution is ≤30μg / L.

[0014] The boric acid washing liquid after the third-level cleaning was tested to be qualified, indicating that during the adsorption process, the impurities could no longer be desorbed from the activated carbon. The gold impurities in the boric acid washing liquid were qualified, indicating that the activated carbon had been cleaned and achieved a good impurity removal and purification effect.

[0015] In some embodiments of the present invention, the metal impurities include at least one of copper, calcium, magnesium, lithium, sodium, potassium, aluminum, chromium, manganese, iron, nickel, tin, titanium, cobalt, zinc, arsenic, zirconium, silver, cadmium, gold, lead, mercury, indium or thallium.

[0016] In some embodiments of the present invention, in step S1, the activated carbon raw material is a wood activated carbon raw material.

[0017] In some embodiments of the present invention, wood activated carbon raw materials are specifically used, which are made from wood raw materials. Compared with coal-based activated carbon made from coal-based raw materials, wood activated carbon has fewer metal impurities and is more suitable for the impurity removal method of the present invention. The wood activated carbon after impurity removal has a good adsorption effect on organic pollutants, which is conducive to the preparation of high-purity electronic-grade boric acid.

[0018] In some embodiments of the present invention, in step S1, the concentration of the dilute sulfuric acid is 0.01 to 10 mol / L; in some embodiments of the present invention, the concentration of the dilute sulfuric acid is 0.03 to 5 mol / L; non-limiting examples are 0.05 mol / L, 0.1 mol / L, 1 mol / L or 3 mol / L.

[0019] In some embodiments of the present invention, in step S2, the conductivity of the ultrapure water is ≤ 1 μS; in some specific embodiments of the present invention, the conductivity of the ultrapure water is 0.1 - 1 μS; non-limiting examples are 0.3 μS, 0.5 μS, 0.7 μS or 0.9 μS.

[0020] In some embodiments of the present invention, in step S2, the total content of metal impurities in the ultrapure water is ≤ 10 μg / L; in some specific embodiments of the present invention, the total content of metal impurities in the ultrapure water is 4 - 10 μg / L; non-limiting examples are 5 μg / L, 6 μg / L, 7 μg / L, 8 μg / L or 9 μg / L.

[0021] In some embodiments of the present invention, in step S1, the volume ratio of dilute sulfuric acid to activated carbon is not limited, as long as the dilute sulfuric acid can submerge the activated carbon.

[0022] In some embodiments of the present invention, in step S2, the volume ratio of ultrapure water to activated carbon is also not limited.

[0023] In some embodiments of the present invention, in step S3, the volume ratio of boric acid solution to activated carbon is (5 - 20):1; in some specific embodiments of the present invention, the volume ratio of boric acid solution to activated carbon is (6 - 15):1; non-limiting examples are 7:1, 8:1, 10:1 or 12:1.

[0024] In some embodiments of the present invention, before cleaning, it further includes the step of filling the activated carbon raw material in an activated carbon column. The two ends of the activated carbon column are open, divided into an upper opening and a lower opening, and are available for liquid to enter and exit.

[0025] In some embodiments of the present invention, the dilute sulfuric acid in step S1 flows in from the upper opening of the activated carbon column and flows out from the lower opening; the ultrapure water in step S2 flows in from the upper opening of the activated carbon and flows out from the lower opening; the boric acid solution in step S3 flows in from the lower opening of the activated carbon column and flows out from the upper opening.

[0026] Both the first - stage and second - stage cleaning adopt the normal washing method of flowing in from the upper part and flowing out from the lower part, while the third - stage cleaning adopts the back - washing method of flowing in from the lower part and flowing out from the upper part. The third - stage cleaning adopting the method of flowing in from the lower part and flowing out from the upper part can keep a specific volume ratio between the boric acid solution and the activated carbon, enabling the boric acid solution to fully clean the activated carbon and achieving a better impurity removal effect.

[0027] The second aspect of the present invention provides an activated carbon obtained by the impurity removal method described in the first aspect of the present invention.

[0028] The activated carbon obtained by the impurity removal method of the first aspect of the present invention has high purity and low metal impurity content.

[0029] The third aspect of the present invention provides an application of the activated carbon described in the second aspect of the present invention in the preparation of electronic-grade boric acid.

[0030] The activated carbon described in the second aspect of the present invention has a low content of metal impurities and will not introduce new metal impurities when used in the preparation of electronic-grade boric acid. Moreover, the wood-based activated carbon after impurity removal has a good adsorption effect on organic pollutants, which is conducive to effectively reducing the total organic carbon (TOC) content in the boric acid product. When this activated carbon is used in the preparation of electronic-grade boric acid, it is beneficial to obtain electronic-grade boric acid with high purity, low metal impurity content and low TOC content.

[0031] The fourth aspect of the present invention provides a method for preparing electronic-grade boric acid, which includes the following steps: passing a crude boric acid solution through an activated carbon column containing the activated carbon described in the second aspect of the present invention for degreasing to obtain a degreased boric acid solution; and subjecting the degreased boric acid solution to purification treatment to obtain the electronic-grade boric acid.

[0032] In some embodiments of the present invention, when degreasing, the residence time of the crude boric acid solution in the activated carbon column is 0.6 - 5 h; in some specific embodiments of the present invention, the residence time of the crude boric acid solution in the activated carbon column is 0.8 - 3 h; non-limiting examples are 0.9 h, 1 h, 1.2 h, 1.5 h, 2 h or 2.5 h.

[0033] The activated carbon provided by the present invention has a good adsorption effect on TOC contained in the crude boric acid solution. When the residence time is more than 0.6 h, the removal rate of TOC can reach more than 60%. When staying for about 1 h, it can reach more than 80%. When staying for 2 h, it can reach more than 90%. By adjusting the residence time, electronic-grade boric acid with less TOC content can be obtained, and this method is simple, efficient and has a good purification effect.

[0034] In some embodiments of the present invention, when degreasing, the pH value of the crude boric acid solution is adjusted to 2 - 5; non-limiting examples are 2.5, 3, 3.5, 4 or 4.5.

[0035] After the activated carbon is cleaned and modified, functional groups such as hydroxyl groups and carboxyl groups are attached to its surface, and the adsorption ability of the activated carbon to organic molecules will change with the change of pH. Therefore, when the pH value of the crude boric acid solution is adjusted to an appropriate level, the activated carbon has a good adsorption and removal effect on TOC. When the pH is too high, the removal rate of TOC will decrease, and metal ions in the solution are likely to precipitate, resulting in product loss. When the pH is too low, the improvement effect on the removal rate of TOC is not obvious, and it will also lead to too high an acid consumption, increasing the cost.

[0036] In some embodiments of the present invention, the activated carbon is granular activated carbon, and the average particle size of the granular activated carbon is 0.5 to 3 mm; in some specific embodiments of the present invention, the average particle size of the granular activated carbon is 0.7 to 2.5 mm; non-limiting examples are 0.8 mm, 1 mm, 1.5 mm or 2 mm.

[0037] Using granular activated carbon can make it contact more fully with the crude boric acid solution, and the specific particle size has a good adsorption effect on impurities, achieving a good purification effect.

[0038] In some embodiments of the present invention, the specific surface area of the activated carbon is 1000 to 1500 m 2 / g; non-limiting examples are 1100 m 2 / g, 1200 m 2 / g, 1300 m 2 / g or 1400 m 2 / g.

[0039] The beneficial effects of the present invention are as follows: The present invention uses a three-stage cleaning method to remove impurities from the activated carbon raw material, and the total content of metal impurities in the obtained activated carbon is low. It has a good effect when used in the preparation process of electronic-grade boric acid, especially can achieve a good TOC removal effect. The activated carbon obtained by the impurity removal method of the present invention has a wide application in the preparation of high-purity electronic-grade boric acid. Description of the Drawings

[0040] Figure 1 It is a process flow chart of the impurity removal method of the activated carbon in Example 1 of the present invention. Detailed Description of the Invention

[0041] The content of the present invention will be further described in detail through specific examples below. It should also be understood that the following examples are only used to further illustrate the present invention and cannot be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the principles described in the present invention all belong to the protection scope of the present invention. The specific process parameters and the like in the following examples are also only an example within a suitable range, that is, those skilled in the art can make selections within a suitable range through the description in this article, rather than being limited to the specific data in the examples below. The raw materials, reagents or devices used in the following examples and comparative examples can be obtained from conventional commercial channels or can be obtained by existing known methods without special instructions.

[0042] The activated carbon raw material of the present invention contains relatively more metal ions. In some embodiments of the present invention, the metal ions in the activated carbon raw material include at least one of copper, calcium, magnesium, lithium, sodium, potassium, aluminum, chromium, manganese, iron, nickel, tin, titanium, cobalt, zinc, arsenic, zirconium, silver, cadmium, gold, lead, mercury, indium or thallium; in some specific embodiments of the present invention, the metal ions in the activated carbon raw material include copper, calcium, magnesium, lithium, sodium, potassium, aluminum, chromium, manganese, iron, nickel, titanium, cobalt, zinc, arsenic, zirconium and lead; in some examples of the present invention, among the metal ions in the activated carbon raw material, the calcium content is 300-400 mg / kg, the magnesium content is 200-300 mg / kg, the potassium content is 7000-8000 mg / kg, and the sodium content is 700-800 mg / kg.

[0043] In the following examples, ND means that when the content of a certain substance is lower than the lowest detection limit of the detection equipment, the substance will be marked as "ND" in the detection report, and the substance cannot be detected, indicating that the content of the substance ≤ 0.01 μg / L.

[0044] Example 1

[0045] This example provides a method for removing impurities from activated carbon. The process flow chart is as Figure 1 shown, and specifically includes the following steps:

[0046] S1. Primary cleaning: Fill the activated carbon raw material in the activated carbon column. The two ends of the activated carbon column are open, divided into an upper opening and a lower opening, which can allow liquid to enter and exit. Pass dilute sulfuric acid through the upper opening to clean the activated carbon raw material and soak it for 20-30 h, and flow out the dilute sulfuric acid washing solution from the lower opening. The activated carbon in the activated carbon column is primary activated carbon. The activated carbon raw material in this step is specifically a commercially available wood-based activated carbon raw material. Compared with the coal-based activated carbon made from coal-based raw materials, the wood-based activated carbon has fewer metal impurities, is suitable for the impurity removal method of the present invention, and the wood-based activated carbon after impurity removal has a good adsorption effect on organic pollutants, which is beneficial to the preparation of high-purity electronic-grade boric acid.

[0047] S2. Secondary cleaning: Pass ultrapure water through the upper opening of the activated carbon column to clean the primary activated carbon, and flow out the water washing solution from the lower opening until the conductivity of the water washing solution ≤ 10 μS. The activated carbon in the activated carbon column is secondary activated carbon. The conductivity of the ultrapure water used in this step is 0.95 μS, and the total content of metal impurities in the ultrapure water is 9.44 μg / L. The metal impurities detected in the ultrapure water are: 4.79 μg / L Ca, 1.49 μg / L Ni, 1.46 μg / L Sn and 1.70 μg / L Zn, and no other metal impurities are detected.

[0048] S3. Tertiary cleaning: Boric acid solution is introduced into the lower opening of the activated carbon column to clean the secondary activated carbon, and the boric acid washing liquid flows out of the upper opening. The volume ratio of boric acid solution to activated carbon is 8:1. The residence time of the boric acid solution in the carbon column is controlled to be 1h. The boric acid solution is used for cleaning until the difference between the total content of metal impurities in the boric acid washing liquid and the total content of metal impurities in the boric acid solution is ≤30μg / L, so as to obtain the activated carbon after impurities are removed.

[0049] Note: The total content of metal impurities (total gold impurities) in this example is the combined content of copper, calcium, magnesium, lithium, sodium, potassium, aluminum, chromium, manganese, iron, nickel, tin, titanium, cobalt, zinc, arsenic, zirconium, silver, cadmium, gold, lead, mercury, indium and thallium.

[0050] After the secondary cleaning, ultrapure water can no longer wash away the metal impurities adsorbed on the activated carbon, and the cleaning limit of ultrapure water for activated carbon has been reached (22.88μg / L). However, some metal impurities are still adsorbed on the activated carbon, and boric acid solution is needed for cleaning. Boric acid is relatively advanced in the adsorption order of activated carbon, and can replace the metal impurities adsorbed in the activated carbon, so that the gold impurities are desorbed from the activated carbon, thereby achieving the effect of further purification of the activated carbon column. The boric acid washing solution after the tertiary cleaning is qualified, indicating that during the adsorption process, the impurities can no longer be desorbed from the carbon column. The metal impurities in the boric acid washing solution are qualified, indicating that the carbon column has been cleaned and a good impurity removal and purification effect has been achieved.

[0051] Application Example 1

[0052] This example provides a method for preparing electronic grade boric acid, which specifically comprises the following steps:

[0053] Take an activated carbon column filled with activated carbon, the actual column length is 175-185 cm, the effective column length is 150-160 cm, the activated carbon is the activated carbon obtained in Example 1 after impurities are removed, and its specific surface area is 1300 m 2 / g, in granular form with a particle size in the range of 0.83 to 2.36 mm, into which crude boric acid solution is introduced for deoiling treatment, the total metal impurity content of the crude boric acid solution is 469 μg / L, and the TOC content is 10.38 mg / L. During the deoiling treatment, the pH value of the solution is 3.9, the flow rate is 50 L / h, and the residence time is 1 h to obtain a boric acid deoiling liquid, which is then purified to obtain electronic grade boric acid.

[0054] During oil removal, the residence time of the crude boric acid solution in the activated carbon column was changed and the TOC removal rate was measured. As shown in Table 1, the pH value of the crude boric acid solution was 3.9 during the process.

[0055] Table 1 Relationship between the residence time of crude boric acid solution in the activated carbon column and TOC removal rate

[0056]

[0057] As can be seen from Table 1, when the residence time of the crude boric acid solution in the activated carbon column is 0.6 - 2 h, it has a good TOC removal effect. When the residence time is more than 0.6 h, the TOC removal rate can reach more than 60%. When the residence time is 1 h, the removal rate can reach more than 80%. When the residence time is 2 h, the removal rate can reach more than 90%. Extending the residence time after 1 h has no obvious effect on the TOC removal effect, mainly because the adsorption capacity of the activated carbon has reached saturation at this time. When the residence time is 2 h, a good TOC removal rate can be achieved, reaching more than 91%. It can be seen that the method for removing TOC using the activated carbon in Example 1 in Application Example 1 is simple, efficient and has a good oil removal effect.

[0058] Testing the obtained electronic-grade boric acid, it can be obtained that the total content of metal impurities such as Fe, Ti, Al, and Ca in the solution is below 49.51 μg / L. The method of Application Example 1 can obtain boric acid with high purity and low impurity content, which can be used as products in the field of nano-scale chip integrated circuits. Especially, using the activated carbon obtained in Example 1 for adsorption and oil removal realizes a good TOC removal effect and does not introduce new metal impurities, ensuring the purity of the final product.

[0059] Application Comparative Example 1

[0060] This example provides a method for preparing electronic-grade boric acid. The difference from Application Example 1 is that the activated carbon filled in the activated carbon column in this example is a commercially available raw wood activated carbon material without cleaning treatment; the pH value of the crude boric acid solution is 3.9, and the residence time of the crude boric acid solution in the activated carbon column is 1 h.

[0061] In the boric acid solution obtained in this example, the total amount of metal impurities such as Fe, Ti, Al, and Ca is 19.36 mg / L, and the TOC content is 2.42 mg / L. It can be seen that directly using the raw wood activated carbon material without cleaning treatment for adsorption and oil removal will introduce more impurities, making it difficult to prepare high-purity electronic-grade boric acid.

[0062] Application Comparative Example 2

[0063] This example provides a method for preparing electronic-grade boric acid. The difference from Application Example 1 is that in this example, no activated carbon column is used for oil removal treatment.

[0064] In the boric acid solution obtained in this example, the total amount of metal impurities such as Fe, Ti, Al, and Ca is 49.59 μg / L, and the TOC content is 10.37 mg / L. It can be seen that without using activated carbon for oil adsorption, the removal effect of TOC is poor; while in Application Example 1, activated carbon is used for oil adsorption, and the total content of metal impurities is basically the same as that in Application Comparative Example 2. That is to say, using the purified activated carbon for oil adsorption in Application Example 1 will not introduce additional metal impurities into the system and can achieve a better TOC removal effect.

[0065] In summary, the present invention uses a three-stage cleaning method to remove impurities from the activated carbon raw material, and the obtained activated carbon has a low total content of metal impurities. It has a good effect when used in the preparation process of electronic-grade boric acid, especially can achieve a good TOC removal effect. The activated carbon obtained by the impurity removal method of the present invention has a wide application in the preparation of high-purity electronic-grade boric acid.

Claims

1. A method for removing impurities from activated carbon, characterized in that: The following steps are involved: S1. Primary cleaning: Use dilute sulfuric acid to clean the activated carbon raw material and soak it for 20 to 30 hours to obtain primary activated carbon; S2. Secondary cleaning: using ultrapure water to clean the primary activated carbon to obtain secondary activated carbon and a washing liquid, wherein the conductivity of the washing liquid is ≤10 μS; S3, tertiary cleaning: washing the secondary activated carbon with a boric acid solution to obtain activated carbon and a boric acid washing solution after impurities removal, wherein the difference between the total content of metal impurities in the boric acid washing solution and the total content of metal impurities in the boric acid solution is ≤30 μg / L; the activated carbon raw material contains metal ions, and the metal ions in the activated carbon raw material include calcium, magnesium, sodium and potassium, wherein the calcium content is 300-400 mg / kg, the magnesium content is 200-300 mg / kg, the sodium content is 700-800 mg / kg, and the potassium content is 7000-8000 mg / kg; In step S3, the volume ratio of the boric acid solution to the secondary activated carbon is (5-20):

1.

2. The impurity removal method according to claim 1, characterized in that: In step S1, the activated carbon is wood activated carbon.

3. The impurity removal method according to claim 1, characterized in that: In step S2, the conductivity of the ultrapure water is ≤1 μS; And / or, in step S2, the total content of metal impurities in the ultrapure water is ≤10 μg / L.

4. The impurity removal method according to claim 1, characterized in that: In step S3, the metal impurities include at least one of copper, calcium, magnesium, lithium, sodium, potassium, aluminum, chromium, manganese, iron, nickel, tin, titanium, cobalt, zinc, arsenic, zirconium, silver, cadmium, gold, lead, mercury, indium or thallium.

5. Activated carbon obtained by the impurity removal method according to any one of claims 1 to 4.

6. Use of the activated carbon according to claim 5 in the preparation of electronic grade boric acid.

7. A method for preparing electronic grade boric acid, characterized in that: The following steps are involved: Passing the crude boric acid solution through an activated carbon column containing the activated carbon according to claim 5 to remove oil and obtain a boric acid deoiled liquid; The boric acid deoiling liquid is purified to obtain the electronic grade boric acid.

8. The preparation method according to claim 7, characterized in that: During oil removal, the residence time of the crude boric acid solution in the activated carbon column is 0.6 to 5 hours.

9. The preparation method according to claim 7, characterized in that: During oil removal, the pH value of the crude boric acid solution is 2-5.

10. The preparation method according to claim 7, characterized in that: The activated carbon is granular activated carbon, and the average particle size of the granular activated carbon is 0.5 to 3 mm.

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